The present invention relates to a device for introducing a spiral blade into an intramedullary nail.
Intramedullary nails are frequently used for internal fixation of long bones such as the femur. These intramedullary nails are often used in conjunction with a locking element for securing the intramedullary nail within the medullary canal. One such locking element is a spiral blade. The intramedullary nail has a borehole for receiving the spiral blade. Because of the spiral blade geometry, the borehole has an elongated cross-section, for instance in the form of a slot or in a keyed opening of similar shape. As the borehole for the spiral blade in the intramedullary nail is only slightly larger than the spiral blade, the spiral blade can be inserted into the nail only at certain rotational angles. As the spiral blade is inserted through the borehole, the spiral blade must rotate about its longitudinal axis to avoid excessive removal of bone. However, in order to align the spiral blade with the elongated borehole in the nail, the spiral blade must be in a specific position when it enters the nail.
With prior art devices for insertion of a spiral blade, a hole would be drilled through the bone until the intramedullary nail is reached so that the proper orientation of the spiral blade could be determined. In so doing, significant bone must be removed. This loss of bone can compromise the stability of the spiral blade when it is inserted.
Thus, there exists a need for an improved spiral blade insertion instrument.
The present invention relates to an insertion instrument for inserting a spiral blade through a borehole in an implanted intramedullary nail. The instrument includes a targeting strap having first and second arms, a guide sleeve operatively associated with the targeting strap and having a first engaging element, and a mandrel having a second engaging element. The first arm of the targeting strap has a through hole, while the guide sleeve has an opening running coaxially with the through hole. The mandrel is slideably receivable in the opening. The first and second engaging elements cooperate to convert an axial force on the mandrel to helical motion of the mandrel such that a spiral blade detachably mounted to the distal end of the mandrel is properly oriented to be received by the borehole.
In order to position and secure the targeting strap to the intramedullary nail, a targeting strap tube insertable in a hole in the second arm receives a connecting member. The first and second engaging elements are positioned with respect to each other so that the mandrel intersects an axis of the targeting strap tube. This axis intersects a central axis of the guide sleeve and runs at an angle thereto.
The proximal end of the mandrel can have a head that has a diameter larger than that of the opening so that the head contacts a proximal end of the guide sleeve when the spiral blade is received in the borehole. The insertion device can also include a limiting element securable on the mandrel for limiting the amount of movement of the mandrel into the opening. In order to provide adjustability, the limiting element is securable on the mandrel in any one of a plurality of positions.
In one embodiment, the first engaging element is a pin extending across the central axis of the guide sleeve and the second engaging element is a spiral groove on the mandrel. The pin engages the spiral groove to allow helical motion of the mandrel. The second engaging element can comprise first and second spiral grooves mutually offset by about 180 degrees on a lateral surface of the mandrel. The first and second spiral grooves pitch can match the pitch of the spiral blade. The first engaging element can include first and second pins extending across the central axis of the guide sleeve and configured and dimensioned so that each of the first and second pins engages one of the first and second spiral grooves.
In another embodiment, the first engaging element is a thread on a lateral surface of the mandrel and the second engaging element is a mating thread on the opening in the guide sleeve.
The insertion instrument can also include a tissue protective sleeve with the guide sleeve attached to the first arm of the targeting strap. The tissue protective sleeve has a bore running coaxially with the central axis. At least a portion of the tissue protective sleeve is slidably received in the opening of the guide sleeve. The tissue protective sleeve can have a handle and the guide sleeve can have a slot. The handle is moveable within the slot to slide the tissue protective sleeve in the opening of the guide sleeve and prevent rotation of the tissue protective sleeve. A lateral surface of the tissue protective sleeve can be provided with indicia for selectable axial positioning. In one embodiment, the mandrel has a shoulder that contacts a proximal end of the tissue protective sleeve when the spiral blade is received in the borehole.
The present invention also relates to an insertion instrument for inserting a spiral blade through a borehole in an implanted intramedullary nail. The instrument comprises a targeting strap having first and second arms and a through hole in the first arm, an alignment element associated with the through hole, and a spiral blade that cooperates with the alignment element to align the blade with the borehole in the nail. In one embodiment, the alignment element comprises a pin.
With the insertion instrument of the present invention, the distance between the intramedullary nail and the end of the spiral blade at the beginning of the guided movement is always the same due to the design of the targeting strap. The spiral blade is positioned so that when it is inserted into the intramedullary nail, the spiral blade has a rotational orientation that corresponds with the geometry of the elongated borehole. This alignment of the spiral blade with the borehole is achieved independently of the width of the condyle, and independently of the entry point of the spiral blade into the bone.
Furthermore, the insertion instrument of the present invention makes it possible for the mandrel to be driven against the bone only so far that the mandrel reaches the bone when the spiral blade is introduced. This precise positioning of the spiral blade in the bone can be accomplished in the following ways:
by eye, without any visual assistance;
by radiology;
by using a monitor and cameras that can be brought close to the bone;
by measuring the distance between the device and the bone and securing a locking ring on the mandrel to function as a stop;
by bringing the mandrel to the bone before installing the spiral blade and at the same time securing a locking ring on the mandrel to function as a stop;
by means of a calibrated tissue protection sleeve around the mandrel which makes the device axially displaceable (the dimension reading on the calibrated tissue protection sleeve is set with the help of a stop on the mandrel which is stopped by the guide sleeve when the spiral blade is received in the borehole, thereby correctly positioning the spiral blade in the axial direction);
by configuring the mandrel to have a larger diameter than the spiral blade and is in contact with the bone when the spiral blade is received by the borehole; and
by designing the tissue protective sleeve around the mandrel to be axially displaceable in the device and to have a length such that the shoulder on the rear end of the mandrel is in contact with this tissue protective sleeve when the spiral blade is introduced into the bone.
The spiral blade is typically inserted with the help of a guide wire which is positioned through a drill bush. The drill bush is inserted coaxially through a groove protective sleeve inserted coaxially into the guide sleeve. The cam groove protective sleeve is inserted into the guide sleeve so that the grooves are not damaged during drilling. The length of the spiral blade is then read on the guide wire and the drill bush is removed. Then the lateral cortex is drilled with a drill which is guided axially by the guide wire with the help of the groove protective sleeve and the tissue protective sleeve. Drilling is continued until the drill reaches the stop provided for this purpose on the groove protective sleeve. The groove protective sleeve is then removed, the position is read by the mark on the tissue protective sleeve, and this position is set as the stop by using the limiting element on the mandrel introducing the spiral blade. The mandrel with the spiral blade attached to it is driven in until the limiting element attached to the mandrel as a stop comes in contact with the guide sleeve, and thus the spiral blade is completely inserted.